VKOR is a member of a large family of predicted enzymes that are present in vertebrates, Drosophila, plants, bacteria and archaea.

[1] Solved bacterial VKOR structures has enabled more insights into the catalytic mechanism.

The quinone to be reduced is bound by a redox-active CXXC motif in the C-terminal helices, similar to the DsbB active site.

Two other cysteines to the N-terminal are located in a loop outside of the transmembrane region; they relay electrons with a redox protein (or in the case of the bacterial homolog, its own fused domain).

Although EC 1.17.4.4 notes both paralogs as having both activities, the precise division of labor in vitro is debated.